Image processing device, image processing method, and image processing circuit

1. An image processing device configured to synthesize a first image and a second image shot in two or more exposure times, the two or more exposure times being different in length, the first image and the second image being shot in a parallel way within one frame time, the image processing device comprising: a level adjuster configured to adjust a luminance level of the first image and output a corrected first image having a luminance level that is substantially same as a luminance level of the second image; a movement detector configured to calculate an absolute value of a difference in a pixel value between each pair of co-located pixels in the corrected first image and the second image and accumulate the absolute value on an image block basis, an image block being a plurality of sets of continuous pixels in the corrected first image or the second image to obtain a movement detection amount in each of a plurality of image blocks; a movement blending ratio calculator configured to smoothen the movement detection amount in each of the plurality of image blocks based on differences in the movement detection amount between adjacent blocks of the plurality of blocks so that a smoothened movement detection amount of each pixel is determined and calculate a movement blending ratio between each pair of the co-located pixels in the image block based on the smoothened movement detection amount of each pixel; and an image synthesizer configured to generate a movement-adaptive image by synthesizing the co-located pixels at the movement blending ratio.

2. The image processing device according to claim 1 , wherein the movement detector determines to include the absolute value as a target of the accumulation when the absolute value exceeds a predetermined threshold, and excludes the absolute value as the target of the accumulation when the absolute value does not exceed the predetermined threshold, and the predetermined threshold is determined according to luminance of at least one pixel in a periphery of a target pixel in the corrected first image.

3. The image processing device according to claim 1 , wherein the movement blending ratio calculator executes smoothening of the movement detection amount in each of the plurality of image blocks by using an inter-block smoothening filter configured to smoothen the movement detection amount on the image block basis between a first plurality of image blocks located near a second plurality of image blocks and an inter-pixel smoothening filter configured to smoothen amounts of detected movements between a plurality of pixels near a target pixel.

4. The image processing device according to claim 1 , further comprising a luminance blending ratio calculator configured to calculate a luminance blending ratio from pixel values of each pair of the co-located pixels in the first image and the second image, wherein the image synthesizer generates a high dynamic range image by synthesizing the co-located pixels in the movement-adaptive image and the first image at the luminance blending ratio.

5. The image processing device according to claim 1 , wherein the first image is an image shot in an exposure time shorter than for the second image, and the movement blending ratio calculator calculates the movement blending ratio to increase a ratio of pixels of the first image to be synthesized to pixels of the second image with an increase of the smoothened movement detection amount.

6. An image processing method for synthesizing a first image and a second image shot in two or more exposure times, the two or more exposure times being different in length, the first image and the second image being shot in a parallel way within one frame time, the image processing method comprising: outputting a corrected first image having a luminance level that is substantially same as a luminance level of the second image by adjusting a luminance level of the first image; calculating an absolute value of a difference in a pixel value between each pair of co-located pixels in the corrected first image and the second image; obtaining a movement detection amount in each of a plurality of image blocks by accumulating the absolute value on an image block basis, an image block being a plurality of sets of continuous pixels in the corrected first image or the second image; smoothening the movement detection amount in each of the plurality of image blocks based on differences in the movement detection amount between adjacent blocks of the plurality of blocks so that a smoothened movement detection amount of each pixel is determined; calculating a movement blending ratio between each pair of the co-located pixels in the image block based on the smoothened movement detection amount of each pixel; and generating a movement-adaptive image by synthesizing the co-located pixels at the movement blending ratio.

7. An image processing circuit for synthesizing a first image and a second image shot in two or more exposure times, the two or more exposure times being different in length, the first image and the second image being shot in a parallel way within one frame time, the image processing circuit comprising: a level adjuster configured to adjust a luminance level of the first image and output a corrected first image having a luminance level that is substantially same as a luminance level of the second image; a movement detector configured to calculate an absolute value of a difference in a pixel value between each pair of co-located pixels in the corrected first image and the second image and accumulate the absolute value on an image block basis, an image block being a plurality of sets of continuous pixels in the corrected first image or the second image to obtain a movement detection amount in each of a plurality of image blocks; a movement blending ratio calculator configured to smoothen the movement detection amount of each of the plurality of image blocks based on differences in the movement detection amount between adjacent blocks of the plurality of blocks so that a smoothened movement detection amount of each pixel is determined and calculate a movement blending ratio between each pair of the co-located pixels in the image block based on the smoothened movement detection amount of each pixel; and an image synthesizer configured to generate a movement-adaptive image by synthesizing the co-located pixels at the movement blending ratio.